manual: update v.reclass.html for either 'rules' or 'column' option to be specified

[agiudiceandrea]

Add a note about the fact that either 'rules' or 'column' option must be specified.

See

grass/vector/v.reclass/main.c

Lines 103 to 107 in 5cb4e43

	if ((!(rules_opt->answer) && !(col_opt->answer)) ||
	(rules_opt->answer && col_opt->answer)) {
	G_fatal_error(_("Either '%s' or '%s' must be specified"),
	rules_opt->key, col_opt->key);
	}

.

[neteler]

Thanks!